Hamid Valipour

Nonlocal Damage Formulation for a Flexibility-Based Frame Element

This paper presents the formulation for a novel flexibility-based one-dimensional (1D) finite element that captures material and structural softening within a reinforced concrete framed structure. Separating the total elastic and inelastic components of the strain at integration points, a secant solution strategy is introduced that is consistent with damage models in the framework of nested iterative algorithms. In this formulation and solution strategy, at every stage of loading the inelastic deformation of the element can be obtained directly without resorting to unloading processes, which is useful when the value of inelastic deformation is required according to some seismic design provisions. In addition, a nonlocal integral damage model, based on averaged strain, has been used to ensure mesh size independent objectivity of local and global responses. The efficiency and accuracy of the formulation is compared with numerical and experimental data with good correlation observed and mesh objectivity demonstrated.

Moment-Rotation Model for Blind-Bolted Flush End-Plate Connections in Composite Frame Structures

AbstractThis paper develops both a three-parameter power model and a Ramberg-Osgood model for quantifying the moment—rotation characteristics of a blind-bolted flush end-plate system that connects a composite beam to a concrete-filled steel tubular (CFST) column in a steel framed building structure. By default, these connections are semirigid, and accurate analyses of structures including them necessitate quantitative knowledge of their moment-rotation response. A detailed three-dimensional (3D) nonlinear-continuum–based finite element model of the connection region including the composite beam, flush end-plate, blind bolts and the concrete-filled steel tube is developed in this paper. This sophisticated FE model can capture the pertinent physical, geometrical, and contact nonlinearities, and its accuracy is verified against experimental data reported elsewhere in the literature. The calibrated FE model is then employed for a parametric study in which the effects of the slab reinforcement ratio, the thick...

Experimental Investigations of Deconstructable Timber–Concrete Composite Beams

AbstractIn conventional timber–concrete composite (TCC) beams, timber joists and concrete slabs are connected permanently; however, the permanent timber–concrete connections can hinder repairing and reusing of structural components and accordingly it reduces the sustainability of construction. This paper deals with development and structural performance of a few novel deconstructable TCC connections that can facilitate recycling and reusing of construction materials. The structural performance of 16 different sets of novel deconstructable TCC connections under shear loads is investigated by push-out tests followed by bending tests on nine TCC beams under service and ultimate loads. The behavior of connections and beams are characterized and the TCC connections with the highest strength and stiffness and feasibility for construction and dismantling are identified.

Structural Response of Timber-Concrete Composite Beams Predicted by Finite Element Models and Manual Calculations

This paper presents the structural response of timber-concrete composite (TCC) beams predicted by finite element models (i.e. continuum-based and 1D frame) and manual calculations. Details of constitutive laws adopted for modelling timber and concrete are provided and application of the Hashin damage model in conjunction with continuum-based FE for capturing failure of timber under bi-axial stress state is discussed. A simplified strategy for modelling the TCC connection is proposed in which the connection is modelled by a nonlinear spring and the full load-slip behaviour of each TCC connection is expressed with a formula that can be directly implemented in the general purpose FE codes and used for nonlinear analysis of TCC beams. The developed FE models are verified by examples taken from the literature. Furthermore, the load-displacement response and ultimate loading capacity of the TCC beams are determined according to Eurocode 5 method and compared with FE model predictions.

A Study on Potential Progressive Collapse Responses of Cable-Stayed Bridges

In this paper, a finite element (FE) model for a cable-stayed bridge designed according to Australian standards is developed and analysed statically and dynamically with and without geometrical nonlinearities. The dynamic amplification factor (DAF) and demand-to-capacity ratio (DCR) in different structural components including cables, towers and the deck are calculated and it is shown that DCR usually remains below one (no material nonlinearity occurs) in the scenarios studied for the bridge under investigation, however, DAF can take values larger than two. Moreover, effects of location, duration and number of cable(s) loss as well as effect of damping level on the progressive collapse resistance of the bridge are studied and importance of each factor on the potential progressive collapse response of the bridgeis investigated.

Fibre-reinforced concrete beam assemblages subject to column loss

Application of steel-fibre-reinforced concrete (SFRC) to partially replace conventional steel reinforcement, particularly the stirrups in beams, has found increasing use in practice. However, the collapse response of SFRC beams (with no stirrups) subject to column loss scenario has not been investigated. Accordingly, four 2/5th scale beam sub-assemblages with SFRC and no stirrups are constructed and tested under a column loss scenario and the potential for steel fibres to replace the stirrups is investigated. The experimental results show that the use of structural steel fibres as a replacement for stirrups has a minor influence on the membrane behaviour of beams as well as the robustness of SFRC frames subjected to column loss. In addition, detailed finite-element models of the assemblages are developed and validated against the experimental data and the validated models are used to investigate the influence of steel bar ductility on the ability of beams to develop tensile membrane action. It is conclude...

Experimental Study of Temperature Effects on Water Vapour Sorption and Moisture Transport Phenomena

Water vapour sorption isotherms (WVSIs) provide a relationship between the mass of adsorbed water within pores and the prevailing relative humidity; they are a reflection of the material microstructure. One aspect of cementitious material WVSIs that has not been firmly established is the effect of elevated temperatures. In this paper, two newly developed multi-chamber WVSI testing apparatus are described. These apparatus have been used to study the adsorption and desorption isotherms and kinetics of HCP and concrete at various temperatures. Results show a two-stage equilibrium process in desorption studies, where the initial stage is associated with diffusive moisture transport, and the second appears associated with a time-dependent loss of hysteresis moisture.

Detecting the Presence of Chloride in Hardened Mortar Using Microwave Non-Destructive Testing

Concrete durability is to a large extent governed by the concrete resistance to the penetration of aggressive substances. One such aggressive substances, present predominantly in marine or coastal environments, is the chloride ion. Chloride in presence of water and oxygen cause corrosion and the measurement of chloride content is an important factor in the detection of early corrosion damage induced by chloride attack. However, there is currently a lack of a reliable nondestructive method to examine the chloride content of the structure in practice. This paper presents the results of an experimental study to investigate the viability of Microwave Non-Destructive Testing (MNDT) to monitor the ingress of the chloride into the concrete. The variations in the electromagnetic properties of mortar specimens with variations in their chloride contents are measured to identify correlations between chloride content and two main electromagnetic properties of mortar; viz. dielectric constant and loss factor. EMPs are measured through two-port measurement performed using a vector network analyzer and S-band rectangular waveguide. The existence of correlations between chloride content of mortar and its electromagnetic properties is confirmed by the preliminary results, highlighting the potential for development of an MNDT technique to monitor the chloride content of concrete in practice.

Effects of moisture exposure on the crosslinked epoxy system: an atomistic study

Diffusion of water into the polymer structures can influence the structure and properties of the polymers. The absorbed water is believed to degrade the strength and properties of the polymers and hence it is important to study how it affects the thermal and mechanical properties of the polymers. In this report, the effects of moisture on the epoxy network and its properties are studied. The epoxy in this work is considered as the result of the curing of diglycidyl ether bisphenol-A (DGEBA) with JEFFAMINE®-D230 hardener. Several structural and dynamics analysis has been conducted to investigate the effects of the ingress of water into the polymer structure. The significant changes in the epoxy structure as a result of introducing water to the system are observed. The molecular structure has been monitored as it underwent the water uptake process. The variation of the atomic correlations due to the exposure to the moisture is reported. Moreover, the effects of adding water on the glass transition temperature and Youngs modulus is revealed. The changes in the properties are explained by the results obtained from monitoring the molecular structure.

Numerical modelling of timber/timber–concrete composite frames with ductile jointed connection

Due to the scarcity of experimental data, this article focuses on the application of detailed finite element models for evaluating structural behaviour of timber–concrete composite frames with post-tensioned beam-to-column joints. In the developed finite element models, nonlinear behaviour and failure mode of timber and concrete under biaxial stress state are captured by hypo-elastic constitutive laws based on the equivalent uniaxial strain concept. In addition to material nonlinearities, the effect of geometrical nonlinearities and nonlinearity of contacts at the concrete slab-to-beam, beam-to-column and slab-to-column interfaces are considered in the finite element models. The accuracy of developed finite element models is verified against available experimental data on post-tensioned timber frames, and the validated analytical tool is used to undertake a parametric study. It is shown that elastic modulus of timber and the details of concrete slab-to-column connection can significantly affect the drift response and failure mode, whereas the compressive strength of timber and stiffness of timber–concrete composite connection have only a minor influence on the drift and failure mode of the timber/timber–concrete composite frames with ductile jointed connections.